Most refrigeration compressors use mineral oil lubricants with chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) refrigerants. In addition to being inexpensive and rugged lubricants, mineral oils are miscible with CFCs and HCFCs, which is important in providing good oil return. In a system with poor oil return, the oil that leaves the compressor collects at various points in the refrigeration system and does not return to the compressor, leading to clogging, poor lubrication, and decreased efficiency.
With the continued regulatory pressure limiting the use of ozone depleting substances, the refrigeration industry has been moving to non-ozone depleting hydrofluorocarbon (HFC) based refrigerants. HFCs, however, lack the miscibility with traditional lubricants such as mineral oils necessary to provide adequate performance. This has resulted in the implementation of oxygenated lubricants such as polyol ester (POE) oil, polyalkylene glycol (PAG) oil, and polyvinyl ether (PVE) oil. These new lubricants can be considerably more expensive than traditional mineral oil lubricants and can be extremely hygroscopic. Their combination with water can result in the undesirable formation of acids that can corrode parts of the refrigeration system and lead to the formation of sludges. Consequently, there is a need and opportunity to resolve this low solubility and oil return problem so that the refrigeration industry may utilize HFC-based refrigerants with mineral oil and/or oxygenated lubricants.
U.S. Pat. No. 6,516,837 discloses a method of introducing refrigerants into refrigeration systems where a chlorine-containing refrigerant is removed while the lubricant is retained and a composition comprising a refrigerant, a surfactant and a solubilizing agent is introduced into the system. The patent discloses that the surfactants and solubilizing agents are needed because many non-chlorine-containing refrigerants, including HFC's, are relatively insoluble and/or immiscible in the types of lubricants traditionally used such as mineral oil and alkylbenzenes or polyolefins.
U.S. Pat. No. 6,299,792 discloses a halogenated hydrocarbon refrigerant composition comprising a halogenated hydrocarbon, oil, an oil-return agent and optionally an oil-return agent carrier. The oil return agents disclosed are random fluorinated copolymers.
The present invention addresses these needs of the refrigeration industry by providing polymeric oil-return agents which create a solution or stabilized dispersion of lubricant oil with HFC, HFO, and/or HCFC-based refrigerants, permitting improved lubricant oil transport through a refrigeration system and lubricant oil return back to the refrigeration system compressor from other refrigeration system zones. The polymeric oil-return agents of the present invention are effective when used in combinations with conventional mineral oils and/or oxygenated oils.